Measuring the physical properties of galaxy components using modern surveys

Bamford, Steven

Most galaxies are fundamentally multi-component stellar systems, primarily comprising a spheroidal bulge and thin disk. These components have largely independent origins, hence separating their properties provides a wealth of additional information with which to constrain models of galaxy development. However, such decompositions are difficult and current methods are not sufficiently developed to allow the routine use of this technique.

In this contribution we introduce the MegaMorph project, which brings together astronomers, statisticians and computer scientists in a concerted attempt to tackle this obstacle to our understanding of the galaxy population. We are developing an accurate, robust tool for measuring the key physical quantities of the separate structural components within galaxies imaged by large multi-band surveys.

The primary focus of our work is the extension of current tried-and-tested galaxy decomposition techniques to fully utilize multiple images obtained at different wavelengths, as routinely produced by modern surveys. Including this colour information in the galaxy fitting process, together with spectral models from stellar populations synthesis codes, enables more robust decompositions in terms of physically meaningful parameters. Other novel improvements planned involve the inclusion of non-parametric components to naturally account for non-smooth galaxy features, quantifying the evidence for including each potential model component, and ensuring our optimisation is both robust and computationally efficient. We plan to consult with the wider statistics and computer science communities to ensure we find the best solutions for each of these problems.